A number of devices, specifically collets and mandrels, have previously been developed which are adapted to grip a workpiece or tool through radial expansion or contraction. Devices of this type are disclosed, for example, in U.S. Pat. Nos. 3,117,797, 3,357,709, 3,357,710, 3,362,721 and 3,731,942. None of these known devices, however, can be utilized for both expansion and contraction. Further, each of these devices is formed as an axially split sleeve having axially extending rows of ramplike cams provided circumferentially therearound, which cams cooperate with similar fixed cams on the workpiece holder, whereby these devices hence require a special and expensive workpiece holder designed specifically for cooperation therewith. Moreover, each of these arrangements is constructed in a manner which renders it tedious to adapt it to grip a workpiece shank or bore of a different size.
U.S. Pat. No. 2,573,928 discloses an arrangement employing axially aligned series of inner and outer rings having cooperating tapered surfaces therebetween, which arrangement may be used for applications requiring either expansion or contraction. U.S. Pat. No. 2,734,749 discloses a similar structural arrangement. However, neither arrangement has been satisfactory in all respects. In particular, the expanding and contracting rings cannot be quickly interchanged with like elements of a slightly different size in order to adapt the arrangement for use with a workpiece shank or bore of a different size, because the arrangement consists of a plurality of separate rings which must be carefully placed in a precise axial and radial relationship with respect to each other during assembly and are not interconnected in any manner which would retain them in this relationship when disassembled. In addition, actuation and release of the device are in practice effected by axial movement of the rings with a "ripple" effect, and the radial movement is therefore not always uniform along the axial length of the device and a release is not always prompt and complete. Moreover, the requisite axial movement of the rings during actuation typically effects axial movement of the workpiece, which in many applications is not desirable.
Accordingly, an object of the present invention is to provide an improved device for gripping a workpiece or tool which can be utilized both in applications requiring radial expansion (such as a mandrel) to grip a bore in the workpiece and in applications requiring radial contraction (such as a collet) to grip a shank of the workpiece, and which will cooperate with smooth, cylindrical surfaces on both the workpiece and the holder.
A further object of the invention is to provide a device, as aforesaid, which can be quickly and easily interchanged with like units to facilitate gripping of different size workpiece shanks and bores, and which can be arranged to provide either some axial movement or no axial movement of the workpiece during expansion or contraction.
A further object of the invention is to provide a device, as aforesaid, which can be actuated smoothly and rapidly, which provides uniform radial movement along its axial length, and which provides a dependable and complete release.
A further object of the invention is to provide a device, as aforesaid, which is relatively simple and inexpensive to manufacture and assemble, is relatively light, is rugged, and requires little or no maintenance.